Loperamide Mimicking Brugada Pattern

The Potential Mechanisms behind Loperamide-Induced Cardiac Arrhythmias Associated with Human Abuse and Extreme Overdose

Loperamide has been a safe and effective treatment for diarrhea for many years. However, many cases of cardiotoxicity with intentional abuse of loperamide ingestion have recently been reported. We evaluated loperamide in in vitro and in vivo cardiac safety models to understand the mechanisms for this cardiotoxicity. Loperamide slowed conduction (QRS-duration) starting at 0.3 µM [~1200-fold (×) its human Free Therapeutic Plasma Concentration; FTPC] and reduced the QT-interval and caused cardiac arrhythmias starting at 3 µM (~12,000× FTPC) in an isolated rabbit ventricular-wedge model. Loperamide also slowed conduction and elicited Type II/III A-V block in anesthetized guinea pigs at overdose exposures of 879× and 3802× FTPC. In ion-channel studies, loperamide inhibited hERG (IKr), INa, and ICa currents with IC50 values of 0.390 µM, 0.526 µM, and 4.091 µM, respectively (i.e., >1560× FTPC). Additionally, in silico trials in human ventricular action potential models based on these IC50s confirmed that loperamide has large safety margins at therapeutic exposures (≤600× FTPC) and confirmed repolarization abnormalities in the case of extreme doses of loperamide. The studies confirmed the large safety margin for the therapeutic use of loperamide but revealed that at the extreme exposure levels observed in human overdose, loperamide can cause a combination of conduction slowing and alterations in repolarization time, resulting in cardiac proarrhythmia. Loperamide's inhibition of the INa channel and hERG-mediated IKr are the most likely basis for this cardiac electrophysiological toxicity at overdose exposures. The cardiac toxic effects of loperamide at the overdoses could be aggravated by co-medication with other drug(s) causing ion channel inhibition.

Risk of Cardiac Lesion with Chronic and Acute Use of Loperamide-An Integrative Review

Loperamide is a synthetic opioid commonly used as an antidiarrheal due to its activation of u-opioid receptors in the myenteric plexus. In therapeutic doses, it inhibits peristalsis and has anti-secretory and anti-motility effects, until metabolized by intestinal and hepatic CYP3A4 and CYP2C8 into inactive metabolites. Furthermore, loperamide also inhibits L-type voltage-gated calcium (Ca²⁺) channels, increases action potential duration, and can induce arrhythmias and even cardiotoxicity, particularly when taken in extremely high doses. Thus, the aim of this study was to perform an integrative review of the available evidence in the recent literature on the cardiac risks of acute and chronic use of loperamide. In electrocardiogram (ECG) analysis, the most common finding was QTc prolongation in 27 cases, followed by QRS prolongation, first-degree atrioventricular (AV) block, torsades de pointes, ventricular tachycardia, and right bundle branch block. As for the symptoms encountered, syncope, weakness, palpitations, lightheadedness, shortness of breath, nausea, vomiting, bradycardia, and cardiac arrest were the most common. Loperamide can inhibit hERG voltage-gated potassium (K⁺) channels (Kv11.1), leading to the prolongation of repolarization, QTc interval prolongation, and increased risk of torsades de pointes. In addition, loperamide can inhibit voltage-gated sodium (Na⁺) channels (Nav1.5), impairing electrical cardiac conduction and potentiating QRS interval widening. Therefore, QTc prolongation, torsades de pointes, and other ECG alterations are of particular concern regarding loperamide toxicity, particularly when overdosed.

A Case Report of Torsade de Pointes and Brugada Pattern Associated with Loperamide Misuse and Supratherapeutic Loperamide Concentrations

BACKGROUND

Loperamide, commonly sold under the brand name Imodium® (Johnson & Johnson, Fort Washington, PA), is a widely available, over-the-counter antidiarrheal medication that possesses µ-opioid agonist properties and can have catastrophic cardiac events when misused or abused. Since the start of the opioid epidemic in the United States, there has been an increasing number of case reports and deaths linking loperamide abuse with cardiac events such as torsades de pointes (TdP) and Brugada syndrome.

CASE REPORT

This case report presents a 22-year-old man who presented in cardiac arrest from polymorphic ventricular tachycardia consistent with TdP and a Type 1 Brugada pattern after intentional loperamide abuse. We discuss this patient's management and the proposed pathophysiology of these two cardiotoxicities, of which, to our knowledge, no previously published case report has displayed both in the same patient after a supratherapeutic loperamide ingestion. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: As the prevalence of opioid dependency and misuse has increased, so, too, has the misuse of un-scheduled medications such as loperamide to achieve central nervous system opioid effects. It is important for the emergency physician to know about and understand loperamide-associated cardiotoxicities such as prolongation of the QRS, unmasking of Brugada patterns, QT prolongation, or ventricular dysrhythmias such as TdP to be able to recognize and treat it.